17 June 2012: The Tubes are on the east facing roof, and there was no choice in the matter - there was a clear easy space on the main roof, and tubes on the south wall elevation would have been easy targets for the hundreds of walkers and children who pass the house along the path near that wall - through a field full of convenient stones. There would also be much longer pipe runs to get the liquid to the point where it goes down to ground. With an east azimuth you have to get used to seeing most of the action happen in the morning, with the sun going from sunrise to midday. After that, the angle is very acute or it is shade.
|Left, Panels mounted on the south wall, as with the Sunbox now.|
Right, panels mounted at 40degs on our east roof, as with the Kingspan Tubes now.
I did a test of the insolation on the two surfaces, and found that the east roof has some advantages. This estimation from PVGIS is mainly for PV, but the two right hand columns show the solar energy falling on each surface, per square metre. Over a year, the insolation per square meter would be 774 kWh/sqm on the vertical surface of my south wall, and it is 913 kWh/sqm on the existing east roof. The ones on the roof have a better view of the sun at midday than the wall mounted ones.
On this basis, I can be content with their position.
|Table of insolation on a south facing roof at 37º |
(for the Nottingham Lat and Long)
showing it to be 11-12% better than the present location on the roof.
Apply the idea to a roof mounted sunbox?
Perhaps, I should also think of how one might build a roof mounted sunbox, one that can be on a roof instead of a wall, a thicker type of enclosure for solar focus swimming pool panels that could be roof mounted. It would not need back insulation, it would need a side frame, and could have a top of either ETFE or of triple skin polycarbonate. It would need to fit to standard fixing rails. This would have to be value engineered as a comparison with a bundle of tubes.